Tobacco-specific nitrosamines (TSNA) are formed from nicotine and related compounds by a nitrosation reaction that occurs during the curing and processing of tobacco, as illustrated in FIG. 1. The nitrosating agent in air-cured tobacco is usually nitrite derived from the reduction of leaf nitrate by the action of microbes during curing, and production of nitrosamine has been shown to correlate to high levels of nitrate/nitrite and nitric oxide (Liang S., Yang J., Zhou J., Yu J., Ma Y., Bai R., Xu F., Yang C. Application of exogenous substances reduces tobacco-specific nitrosamines content by regulating biosynthesis of nicotine and nitrite in burley tobacco. Acta Physiol. Plant. (2013) 35: 3027-3036; Shi H., Wang R., Bush L. P., Yang H., Fannin F. F. The relationships between TSNAs and their precursors in burley tobacco from regions and varieties. Journal of Food, Agriculture & Environment (2012) 10 (3&4): 1048-1052). TSNA reduction is a desirable aim for the tobacco industry.
Nitrogen (N) and nitrate (NO3−) availability regulate many aspects of plant metabolism, growth and development. The plant-specific lateral organ boundaries domain (LBD) gene family is essential to the regulation of plant lateral organ development and is also involved in the regulation of nitrogen metabolism. Three N/NO3−-induced members of the LBD gene family of transcription factors (LBD37, LBD8 and LBD39) act as negative regulators of anthocyanin biosynthesis in Arabidopsis thaliana (Rubin G., Tohge T., Matsuda F., Saito K., Scheible W-R. Members of the LBD Family of transcription factors repress anthocyanin synthesis and affect additional nitrogen responses in Arabidopsis. Plant Cell (2009) 21 (11): 3567-3584). It is thought that LBD37-39 signal N availability to the plant system, leading to repression of specific N deficiency responses, such as anthocyanin synthesis. The LBD genes also repress many other known N-responsive genes, including key genes required for NO3− uptake and assimilation, resulting in altered NO3− content, nitrate reductase activity/activation, protein, amino acid and starch levels, anthocyanin biosynthesis and N-related growth phenotypes (Rubin et al., 2009).